This invention relates generally to color flat panel displays and, more particularly, to an electroluminescent flat panel display with a resistive touch sensitive panel.
Modern electronic devices provide an increasing amount of functionality with a decreasing size. By continually integrating more and more capabilities within electronic devices, costs are reduced and reliability increased. Touch screens are frequently used in combination with conventional soft displays such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma displays and electroluminescent displays. The touch screens are manufactured as separate devices and mechanically mated to the viewing surfaces of the displays.
There are three common types of resistive touch screens, 4-wire, 5-wire, and 8-wire. The three types share similar structures. FIG. 1a shows a top view of a resistive touch screen 10 and the external circuitry to which it is connected. FIG. 1b shows a side view of the resistive touch screen 10. The touch sensitive elements 14 of the resistive touch screen 10 includes a lower circuit layer 20; a flexible spacer layer 22 containing a matrix of spacer dots 24; a flexible upper circuit layer 26; and a flexible top protective layer 28. All of these layers are transparent. The lower circuit layer 20 comprises conductive materials placed on a substrate 12, forming a circuit pattern.
The main difference between 4-wire, 5-wire, and 8-wire touch screens is the circuit pattern in the lower circuit layer 20 and in the upper circuit layer 26, and the means for making resistance measurements. An external controller 18 is connected to the touch screen circuitry via cable 16. Conductors in cable 16 are connected to the circuitry within the lower circuit layer 20 and the upper circuit layer 26. The external controller 18 coordinates the application of voltages to the touch screen circuit elements. When a resistive touch screen is pressed, the pressing object, whether a finger, a stylus, or some other object, deforms the top protective layer 28, the upper circuit layer 26, and the spacer layer 22, forming a conductive path at the point of the touch between the lower circuit layer 20 and the upper circuit layer 26. A voltage, called a touch coordinate voltage, is formed in proportion to the relative resistances in the circuit at the point of touch, and is measured by the external controller 18 connected to the other end of the cable 16. The controller 18 then computes the (X,Y) coordinates of the point of touch. For more information on the operation of resistive touch screens, see xe2x80x9cTouch Screen Controller Tipsxe2x80x9d by Osgood et al., Application Bulletin AB-158, Burr-Brown, Inc. (Tucson, Arizona).
The external controller 18 is typically an integrated circuit soldered to a printed circuit board 30. Cable 16 is plugged into a connector 32 that is also soldered to the printed circuit board 30. The conductors in the cable 16 connect to the external controller 18 via traces that are placed on the printed circuit board 30 that run between the external controller 18 and the connector 32.
External controller 18 consists of three sub-circuits: a voltage application circuit 34, a touch detection circuit 36, and a multiplexing circuit 38.
The voltage application circuit 34 selects the placement of voltages on the touch screen""s electrodes. The touch detection circuit 36 monitors the voltage read from the touch screen, decides when a touch has been performed, and computes the (X, Y) coordinates of the touch point. The (X, Y) coordinates of the touch point are then transferred to another integrated circuit 39 on the circuit board, often a microprocessor. External controllers are available commercially, for example, the ADS7846 by Texas Instruments (Dallas, Tex.).
As shown in FIG. 2, the touch detection circuit 36 often contains an analog-to-digital converter 40 and a computation circuit 42. Analog-to-digital converter 40 converts the analog voltage measured at the point of touch to a digital value. The computation circuit 42 is often an embedded processor or other circuit that can monitor the digital voltage value, detect the presence of a touch based on the voltage value, and compute the coordinate of the touch based on the magnitude of the digital voltage value. Other processing may be performed, such as averaging to minimize noise.
The multiplexing circuit 38 in FIG. 1a determines which conductors in the cable 16 are routed to the voltage application circuit 34 and to the touch detection circuit 36. This routing changes for determining the X and Y coordinates. The external controller 18 is usually responsive to a clock generated on the printed circuit board 30, and also has voltage inputs. The cable 16 would contain four conductors for 4-wire touch screens, five conductors for 5-wire touch screens, and eight conductors for 8-wire touch screens. The multiplexing circuit 38 would have two wires going to the voltage application circuit 34 and two wires going to the touch detection circuit 36 for 4-wire touch screens. The multiplexing circuit 38 would have four wires going to the voltage application circuit 34 and one wire going to the touch detection circuit 36 for 5-wire touch screens.
FIG. 3 shows a cross section view of a typical prior art electroluminescent display such as an organic light emitting diode (OLED) flat panel display 70 of the type shown in U.S. Pat. No. 5,937,272, issued Aug. 10, 1999 to Tang. The OLED display includes a substrate 72 that provides mechanical support for the display device, a transistor switching matrix layer 74, a light emission layer 78 containing materials forming organic light emitting diodes, and a cable 80 for connecting circuitry within the flat panel display to external controller 81. The substrate 72 is typically glass, but other materials, such as plastic, may be used. The transistor switching matrix layer 74 contains a two-dimensional matrix of thin film transistors (TFTs) 76 that are used to select which pixel in the OLED display that receives image data at a given time. The thin film transistors 76 are manufactured using conventional semiconductor manufacturing processes, and therefore extra thin film transistors 76 may be used to form circuitry for a variety of uses. As mentioned in U.S. Serial No. 09/774,221 filed Jan. 30, 2001, by Peldman et al., the presence of TFTs within an active matrix flat panel display allow functions other than display functions to be implemented on the same substrate as the display function, producing a system-on-panel. The OLED display is responsive to control signals generated by external controller 81. These control signals typically include a pixel clock (sometimes called a dot clock), a vertical synchronization signal (VSYNC), and a horizontal synchronization (HSYNC) signal.
Conventionally, when a touch screen is used with a flat panel display, the touch screen is simply placed over the flat panel display, and the two are held together by a mechanical mounting means such as a frame. FIG. 4 shows such an arrangement with a touch screen mounted on an OLED flat panel display. After the touch screen and the OLED display are assembled, the two substrates 12 and 72 are placed together in a frame 82, often separated by a mechanical separator 84. The resulting assembly contains two cables 16 and 80 that connect the touch screen and the flat panel display to external controllers 18 (see FIG. 1a) and 81 (see FIG. 3).
U.S. Serial No. 09/826,194, filed Apr. 4, 2001 by Siwinski et al. proposes a device in which an organic electroluminescent flat panel display is integrated with a touch screen, sharing a common substrate. This invention has advantages over existing touch screen and flat panel display combinations with decreased cost, no integration steps, decreased weight and thickness, and improved optical quality.
As mentioned above, an external controller 18 controls conventional resistive touch screens. Such resistive touch screens are manufactured for simplicity, and therefore do not contain semiconductor circuitry, such as thin film transistors, that can be used to implement a touch screen controller on the touch screen itself.
Conventionally, all signals controlling a touch screen and an active matrix flat panel display are brought into each device via conductors in two cables. Since there is similarity between the operation of a flat panel display and a touch screen, there is redundancy within the signals brought into the devices. This redundancy results in redundant conductors in the cables, adding to cable cost, and providing increased opportunities for noise to enter the devices via these conductors. Additionally, the associated connector or connectors on the printed circuit board contain redundant pins, further increasing system cost and opportunities for electronic noise injection.
There remains a need therefore for an improved touch screen-flat panel display system that minimizes device weight, removes redundant materials, decreases cost, eliminates special mechanical mounting design, and increases reliability.
The need is met according to the present invention by providing an organic electroluminescent display with integrated touch screen, that includes: a transparent substrate having two faces; a transistor switching matrix and a light emitting layer forming an active matrix electroluminescent display located on one face of the substrate for emitting light through the substrate; touch sensitive elements of a touch screen located on the other face of the substrate; components of a touch screen controller located on the one face of the substrate, and a electrical connector for connecting the components of the touch screen controller on the one face of the substrate to the touch screen elements on the other face of the substrate.
The present invention has the advantage that the number of conductors for making external connection to the device are minimized, thereby minimizing device weight, removing redundant materials, decreasing cost, eliminating special mechanical mounting design, and increasing reliability